There is proposed a system called Adaptive Front-lighting System (AFS), which turns an illumination direction of a headlamp in the transverse direction in accordance with a variation in the steering angle of a steering wheel so as to improve safety in driving an automobile. According to this system, it is advantageous in that the illumination direction of the headlamp can be turned to a direction steered by a driver, that is, a direction in which an automobile travels in addition to the forward direction and the driving safety may be improved.
However, when the illumination direction of the headlamp is controlled based on only the steering angle, a problem may arise in that glare may influence an oncoming vehicle or a preceding vehicle existing in front of an own vehicle. For this reason, it is desirable that the system is configured to detect the oncoming vehicle or the preceding vehicle and the illumination direction of the headlamp is controlled to be aligned to a direction facing a shoulder or a down direction when detecting the oncoming vehicle or the preceding vehicle.
As a technique to detect the oncoming vehicle or the preceding vehicle, there is known a technique that captures an image of a forward area of an own vehicle by using an image capturing camera and analyzes the captured image. In the technique of analyzing the captured image, at day time, the oncoming vehicle or the preceding vehicle can be recognized through an outline obtained by performing, for example, a SOBEL calculation or the like on an image. However, in night time, it is difficult to use this technique.
For this reason, a technique may be conceivable in which the oncoming vehicle or the preceding vehicle is recognized through a bright point in the captured image, the bright point corresponding to the light of the tail lamp of the preceding vehicle or the light of the headlamp of the oncoming vehicle. For example, a color of an origin of the captured image is detected in such a manner that white or color substantially the same as that is recognized as the light of the headlamp of the oncoming vehicle and red is recognized as the light of the tail lamp of the preceding vehicle.
However, since street lamps emitting light by itself or delineators indicating a shoulder by reflecting the light of the headlamp of the own vehicle exist in the road, these lights should be distinguished. As a technique for distinguishing these lights, there is proposed a technique of using an optical flow. For example, JP-A-2007-334859 discloses a technique capable of detecting a stationary object or a moving object by using an optical flow. Accordingly, it is possible to detect the oncoming vehicle or the preceding vehicle by detecting only the moving object excluding the stationary object.
In a case where the street lamps or the delineators are detected by using the optical flow as described in the document, JP-A-2007-334859, it is important to recognize a vanishing point obtained when the bright point for obtaining the optical flow moves from one point toward a specific point in the image and vanishes at the specific point.
For example, FIG. 8 is a schematic diagram showing a captured image of a front area of the own vehicle traveling in a straight two-lane road, where an own lane line L1 and an own-lane-side shoulder line L2 form an own lane on the left side of a center line CL, an opposite lane line L3 and an opposite-lane-side shoulder line L4 form an opposite lane, street lamps LL are arranged at the high positions along the two shoulder lines L2 and L4, and delineators DL are arranged at the low positions. The street lamps LL arranged at the higher positions than the image capturing camera of the own vehicle are photographed at the higher position than the horizontal line H, and the delineators arranged at the lower positions than the image capturing camera of the own vehicle are photographed at the lower position than the horizontal line H.
In a case where the own vehicle travels in the straight road, since the vanishing point of each optical flow shown by the movement locus of the origin of each of the street lamps LL or the delineators DL faces the forward direction, that is, the center position between the horizontal line and the vertical line in the captured image, it is possible to determine the optical flow of each of the street lamps or the delineators. However, as described below, in the case of the curved road in which the road is curved toward the right or left or the case of the uphill road or downhill road, the vanishing point does not face the center position in the image. In this case, it is difficult to determine the attribute of the optical flow, that is, the street lamps or the delineators by using only the vanishing point.
Likewise, in a case where the vanishing point faces the forward direction, it is possible to highly precisely determine that the optical flow has the attribute of the street lamps or the delineators. However, in the case where the vanishing point faces a direction other than the forward direction, it is difficult to determine the attribute of the optical flow. In this case, the road information is obtained so as to know whether the road is the curved road, the uphill road, or the downhill road, and the attribute of the bright point is determined in consideration of the obtained road information.
It may be supposed that road information of a navigation unit is used as the road information. However, the accuracy of the road information of the navigation unit is low, and particularly in the curved road, the curvature radius of the curved road is not highly precisely obtained from the road information of the navigation unit. As a result, since it is difficult to determine whether the optical flow is disposed along the road, it is difficult to determine the attribute of the optical flow in high reliability. For this reason, it is difficult to reliably detect the oncoming vehicle or the preceding vehicle traveling in the curved road, the sloping road, or the like, and difficult to appropriately control the headlamp.